1. Field of the Invention
The present invention relates to a position controller for an optical element.
2. Description of the Related Art
A type of image shake correcting mechanism (shake reduction mechanism/image stabilizing mechanism) which moves an optical element such as a lens element or an image sensor (image pickup device) in a plane orthogonal to an optical axis of an optical system (this optical element is hereinafter referred to as an image-shake-correcting optical element) to reduce image shake in an optical device such as a camera has been often used in recent years. In addition, an invention devised to achieve an improvement in utilization of an optical element accommodation space when the optical device is in a non-operating state, especially to achieve a reduction in thickness of the optical system in the optical axis direction has been proposed.
The image shake correcting unit incorporated in a retractable lens disclosed in Japanese Unexamined Patent Publication 2006-146125 is provided with a lens holder which holds the first lens (designated by the reference numeral 25 in the specification) serving as an image-shake-correcting optical element and an electromagnetic actuator for driving this lens holder in orthogonal directions in a plane orthogonal to an optical axis. In addition, when the retractable lens is fully retracted, the lens holder that holds the first lens is moved to a predetermined off-axis removed (displaced) position by the electromagnetic actuator, and a reduction in length of the photographing optical system is achieved by moving the second lens (designated by the reference numeral 24 in the specification) into space that is created by the displacement of the first lens to the off-axis removed position.
In the imaging device disclosed in Japanese Unexamined Patent Publication 2006-154674 (U.S. Pat. No. 7,630,618 B2), a movable frame which supports an image sensor, which is provided as an image-shake-correcting optical element and is movable in a direction orthogonal to an optical axis of an imaging optical system, is moved by a mechanism for image shake correction within an anti-shake driving range in which the image sensor is positioned on the optical axis in a ready-to-photograph state, and the same movable frame is moved by another mechanism for displacement driving to move the image sensor from a position on the optical axis to an off-axis removed position (displaced position) away from the optical axis when the imaging device moves to the accommodated state. In a non-operating state of the imaging device, a reduction in length of the imaging optical system in the optical axis direction thereof is achieved by positioning the anti-shake correcting optical element (image sensor) that is displaced to the off-axis removed position and another optical element (e.g., a lens group) which remains on the optical axis in a plane orthogonal to the optical axis. As a specific structure therefor, a guide shaft is provided for guiding the movable frame from the anti-shake driving range to the removed position, and the aforementioned another mechanism for displacement driving is configured from a swing member which gives the movable frame a moving force in a direction along the guide shaft.
In the above-mentioned Japanese Unexamined Patent Publication 2006-146125, since the displacing movement of the first lens is performed by an electromagnetic actuator, the amount of the displacing movement of the first lens is limited within the range of the driving amount of the electromagnetic actuator. The displacing movement of the first lens by the electromagnetic actuator is determined according to various conditions such as specifications of the coils and the magnets of the electromagnetic actuator and the positional relationship therebetween; however, it is not possible to apply a large driving amount to the electromagnetic actuator which is so great that the coils and the magnets become largely displaced from each other. For instance, in the structure disclosed in the above-mentioned Japanese Unexamined Patent Publication 2006-146125, due to the limitation on the driving amount of the electromagnetic actuator, the first lens and the lens holder therefor cannot be removed from an optical axis by an amount which is large enough as to allow the whole of the second lens and the lens holder therefor to enter the space on the optical axis from which the first lens and the lens holder therefor have been removed. This limits the effect on reduction in length of the imaging optical system.
In the above-mentioned Japanese Unexamined Patent Publication 2006-154674, since the imaging device disclosed therein is equipped with a mechanism for displacement driving independently of the mechanism for image shake correction, there is no limitation on the driving amount of the electromagnetic actuator, so that an image sensor as an image-shake-correcting optical element and a holding device which holds the image sensor can be given a great amount of movement in a direction to make the image sensor and the holding device therefor removed from an optical axis.